[Improve][Flink]supports multiple parallelisms and remove flink-specific logic from API

[CloverDew]

Purpose of this pull request: Fixes #9980

Problem

After implementing CDC schema evolution support in Flink engine, several issues were identified:

1. The coordinator's state resides in the TaskManager's JVM; if a job fails and restarts, this state is easily lost.
2. Flink's proprietary implementation logic should not be placed in the public API SupportSchemaEvolutionSinkWriter. Furthermore, flush requires manual API implementation.
3. Multi-parallelism configuration is not supported.

Solution

This PR made some minor adjustments to the architecture.:

• BroadcastSchemaSinkOperator operator is introduced to solidify the response state.
• Coordinator is only responsible for communication: pure messenger, stateless.
• Flushing is guaranteed by checkpoints, not manual implementation

Key Changes:

1. Enhanced LocalSchemaCoordinator

• JobId isolation: Prevents multi-job interference using Map<String, WeakReference<LocalSchemaCoordinator>>
• Pure messenger: No persistent state, only temporary communication futures

3. Streamlined BroadcastSchemaSinkOperator

• Idempotency: tracks lastProcessedEpoch using Flink state

4. API Compliance (Addresses #9980)

• API separation: SupportSchemaEvolutionSinkWriter contains only generic applySchemaChange() method
• Flink-specific logic moved: All coordination logic moved from API to Flink translation layer

Testing

• Verified MySQL CDC → MySQL sink schema evolution scenarios
• Confirmed no data loss during schema changes
• Tested multi-job concurrent execution

Breaking Changes

None. This is a refactoring that maintains API compatibility while improving internal implementation.

Related Issues

• Fixes [Bug][Flink] Move Flink-specific flush coordination from API to translation layer #9980: Move Flink-specific flush coordination from API to translation layer.
• To address the issue of state loss, an operator-held state mechanism is introduced.
• Multi-parallelism is already supported.

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  [New License Guide](https://github.com/apache/seatunnel/blob/dev/docs/en/contribution/new-license.md)
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If necessary, please update incompatible-changes.md to describe the incompatibility caused by this PR.
• If you are contributing the connector code, please check that the following files are updated:
  1. Update [plugin-mapping.properties](https://github.com/apache/seatunnel/blob/dev/plugin-mapping.properties) and add new connector information in it
  2. Update the pom file of [seatunnel-dist](https://github.com/apache/seatunnel/blob/dev/seatunnel-dist/pom.xml)
  3. Add ci label in [label-scope-conf](https://github.com/apache/seatunnel/blob/dev/.github/workflows/labeler/label-scope-conf.yml)
  4. Add e2e testcase in [seatunnel-e2e](https://github.com/apache/seatunnel/tree/dev/seatunnel-e2e/seatunnel-connector-v2-e2e/)
  5. Update connector [plugin_config](https://github.com/apache/seatunnel/blob/dev/config/plugin_config)

[LiJie20190102]

thx, please use org.apache.seatunnel.common.constants.JobMode#STREAMING instead of STREAMING